The early hormone environment has been thought to influence the development of male/female behavioral and neuroendocrine differences through the life span. This study exposed developing male and female rhesus monkeys to atypical prenatal hormonal environments and has been investigating their behavioral and neuroendocrine development. Treatments were designed to mimic accidental exposure to or suppression of androgens prenatally. Females that received increased prenatal androgen were not altered anatomically, appearing as typical females. Their neuroendocrine function was modified with a decreased sensitivity to GnRH during their first 2 mo of life. In contrast, females exposed to an androgen receptor blocker (flutamide) displayed increased sensitivity to GnRH suggesting that rhesus females are naturally exposed to moderate levels of prenatal androgen, probably of maternal origin. Males exposed to flutamide also showed increased sensitivity to GnRH, although al l males we re more responsive than all females. During infancy males and females differed in their pattern of vocalizations, with females being more vocal and using more call types. Prenatal hormonal treatment affected infant vocalizations such that exposure to increased androgen resulted in females that displayed a more male-like call pattern. These vocal differences suggest that prenatal androgen exposure may effect emotionality, a notion currently under investigation. FUNDING NIMH / MH 50268-04 $151,003 12/01/97 - 11/31/98 PUBLICATIONS *Tannenbaum, P.L. and Wallen, K. Sexually initiated affiliation facilitate rhesus monkey integration. Annals of the New York Academy of Sciences 807:578-582, 1998. *Zehr, J.L., Maestripieri, D.M. and Wallen, K. Estradiol increases female sexual initiation independent of male responsiveness in rhesus monkeys. Horm. Behav. 33:95-103, 1998. P51RR00165-38 1/1/98 - 12/31/98 Yerkes Regional Primate Research Center